S-adenosyl-L-methionine-dependent protein-arginine N-methyltransferase that catalyzes both the mono- and asymmetric (type I) dimethylation of the guanidino nitrogens of arginine residues in a variety of RNA-binding proteins such as heterogeneous nuclear ribonucleoproteins (hnRNPs) and small nuclear ribonucleoproteins (snRNPs) (PubMed:8668183, PubMed:8647869). Methylates NAB2, NPL3, HRP1 and YRA1, shuttling hnRNPs involved in mRNA processing and export, facilitating their export out of the nucleus (PubMed:8668183, PubMed:9499403, PubMed:10652296, PubMed:11779864, PubMed:15314027). Methylation of NPL3 weakens its interaction with THO2, a component of the TREX (transcription/export) complex important for transcriptional elongation and recruitment of mRNA export factors (PubMed:15314027, PubMed:20053728). Methylates the hnRNP HRB1, but does not influence its subcellular location (PubMed:9499403). Methylates the nucleolar proteins GAR1, NOP1 and NSR1 (PubMed:12756332). Methylates the snRNP SNP1 and modulates the cotranscriptional recruitment of splicing factors (PubMed:20823272). Dimethylates free histone H4 (HHF1/HHF2) at 'Arg-4' (H4R3me2a) and plays a role in preservation and establishment of silent chromatin domains (PubMed:12097318, PubMed:17158743). Mono- and dimethylates ribosomal protein S2 (RPS2) at 'Arg-11' (PubMed:20035717). Methylates the catalytic subunit of the SWI/SNF chromatin-remodeling complex SNF2 (PubMed:22997150).